The invention relates to a method of producing a conical honeycomb body having a conical foil assembly formed from structured arcuate sheet-metal foils that have been wound and/or stacked to form the conical foil assembly. The foil assembly is then inserted into a casing tube and the sheet-metal foils are fixed by a mechanical clamping aid. The invention further relates to such a honeycomb body. The honeycomb bodies are used in particular as catalyst support structures in exhaust systems of motor vehicles with an internal combustion engine.
Such a conical honeycomb body, with an axis and a casing tube which is conical in relation to the latter and into which a foil assembly wound about the axis in an involute manner is fitted, is known for example from European Patent EP 0 635 097 B1. The foil assembly has a multiplicity of sheet-metal foils, which are stacked one on top of the other and some of which are structured. Each sheet-metal foil is formed in the manner of a ring segment, so that it is delimited by an outer arc which is approximately circular with respect to a central point and an inner arc which is approximately circular, is concentric with respect to the outer arc and lies between the latter and the central point. Each structured sheet-metal foil has corrugations. The corrugation of a sheet-metal foil does not have a constant corrugation height over the entire sheet. The corrugation height must increase from a smaller corrugation height at the smaller arc delimiting the sheet-metal foil to a greater corrugation height at the larger arc delimiting the sheet-metal foil. The ratio of the corrugation heights must correspond approximately to the ratio of the corrugations of the arcs in order that an approximately conical honeycomb body is produced when the sheet-metal foils are intertwisted.
For this purpose, after they have been laminated and/or wound to form a conical foil assembly, which has passages through which a fluid can flow, the in some cases structured, arcuate sheet-metal foils are introduced into the conical casing tube with a first end opening and a second end opening, the first end opening having a larger diameter than the second end opening, are fixed by mechanical clamping aids and are subsequently connected at least partially to one another and to the casing tube by a joining technique, in particular they are soldered.
In this case, the fixing of the conical foil assembly in the conical casing tube is sometimes difficult to perform before the connection by a joining technique. Since, furthermore, the type of fixing may have an influence on the stability of the conical honeycomb body, which is particularly important wherever conical honeycomb bodies are used extremely close to the engine, this fixing does however take on particular significance.
For fixing a conical foil assembly in a conical casing tube it is known to insert two pins, offset radially by 180xc2x0, through the casing tube and the foil assembly and subsequently weld them to the casing tube. It is disadvantageous here that the pins close a certain number of honeycombs of the foil assembly, or deform them in the outer region. In addition, the insertion and welding of pins increases the production costs of such a honeycomb body.
Winding forks, which are connected to one another in such a way that a U shape is obtained, are also known. After the conical foil assembly has been wound and introduced into the conical casing tube, a flat steel plate that has bores at the same spacing as the winding forks is pushed over the winding forks. The winding forks are clamped on the flat steel plate by screws. However, the connection of the two winding forks may cause damage to the conical foil assembly during tightening.
To avoid deformations in particular, externally applied clamping devices, by which the casing tube and foil assembly are clamped, are possible. Owing to the temperatures in the soldering oven, however, the clamping tools must be made to be very robust. Such configurations have the effect of reducing the number of parts per batch. This leads to increased costs in the soldering process. The frequency of use of the clamping tools is also limited by the temperatures in the soldering oven.
Finally, known from the above-cited European Patent EP 0 635 097 B1 for fixing the conical foil assembly are retaining structures which are applied to the conical casing tube. The retaining structure may preferably be a lip running completely around the casing tube; such a lip may be formed, for example, by flanging of the casing tube, but it may also be a separate welded-on component. Another possibility for the retaining structure is a clip that is integrally connected, in particular welded, to the conical casing tube and reaches over the end face. Such a clip is disposed such that it is centered on the end face, so that it touches the central point of the latter. A clip disposed in such a way also has a disadvantageous effect, in particular on the flow characteristics of the exhaust gas to be cleaned.
It is accordingly an object of the invention to provide a conical honeycomb body and a method of producing it, that overcomes the above-mentioned disadvantages of the prior art methods and devices of this general type, with the intention of making the conical honeycomb body easier to produce and/or more stable by the simplest possible fixing of a conical foil assembly in a conical casing tube.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a conical honeycomb body. The method includes the step of forming a conical foil assembly having passages formed therein through which a fluid can flow. The conical foil assembly is formed from arcuate sheet-metal foils being at least one of stacked and wound to form the conical foil assembly. At least some of the arcuate sheet-metal foils are structured sheet-metal foils. The conical foil assembly is introduced into a conical casing tube having a first end opening and a second end opening. The first end opening has a given diameter being larger than a given diameter of the second end opening. The conical foil assembly is fixed in the conical casing tube using a mechanical clamping aid. The mechanical clamping aid is disposed in the conical casing tube at a distance from the first end opening and the second end opening and, at least in portions, the mechanical clamping aid has an annular form. Subsequently, the arcuate sheet-metal foils are connected, at least partially, to one another and to the conical casing tube by a joining technique.
The fact that clamping aids are disposed in the conical casing tube at a distance from its end openings and are configured such that, at least in certain portions, they are of an annular form, simplifies the production of the conical honeycomb body, and at the same time facilitating the later welding into an exhaust system, since the ends are free of additional in-built components. In addition, the stability of the finished body is improved.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a conical honeycomb body containing a conical casing tube having a first end opening and a second end opening. The first end opening has a given diameter and the second end opening has a given diameter being smaller than the given diameter of the first end opening. A conical foil assembly is disposed in the conical casing tube and is formed of arcuate sheet-metal foils being at least one of stacked and wound. At least some of the arcuate sheet-metal foils are structured sheet-metal foils and the arcuate sheet-metal foils are at least partially connected to each other and to the conical casing tube. The conical foil assembly further has passages formed therein through which a fluid can flow. A mechanical clamping aid is disposed in the conical casing tube at a distance from the first end opening and the second end opening and, at least in certain portions, has an annular form. The mechanical clamping aid fixes the conical foil assembly in the conical casing tube.
For this purpose, in a first embodiment, the casing tube has at a distance from the first end opening on its inner side a mechanically fixable ring, or at least mechanically fixable segments of a ring, with the result that the conical honeycomb body can in particular also be produced inexpensively.
Alternatively, the casing tube has at a distance from the first end opening a constriction, as a result of which, as in the case of the solutions with a ring as well, a type of air-gap insulation is produced, with the effect that the temperature of the casing tube does not increase too much during operation under load in a motor vehicle.
The casing tube may also have at a distance from the first end opening an outer bead, in which a prestressed ring can be disposed in a reversibly mechanical manner or by an irreversible joining technique, whereby, as in the case of the other solutions as well, the end openings of the casing tube remain free and can be welded well and easily to other components of an exhaust system.
The casing tube may also have at a distance from the first end opening an inner bead, with an axial force being exerted on the casing tube after the foil assembly has been introduced into the casing tube, the inner bead being deformed in such a way that the foil assembly is fixed in the casing tube. An inner bead, initially of an only relatively flat configuration, allows foil assemblies with a particularly high prestress also to be introduced easily into the casing tube and nevertheless to be fixed well.
A further solution provides that the casing tube has at a distance from the end openings an outer shoulder in corresponding to a width of the foil assembly. This solution is distinguished not only by improving its suitability for being welded in but in particular by good mechanical stability in the finished state of the conical honeycomb body.
Finally, the casing tube and the foil assembly may have a tongue-and-groove system. The casing tube having at a distance from the end openings, in the region of the maximum width of the foil assembly, at least one outer bead. Some of the structured arcuate sheet-metal foils are produced in such a way that at least one detent running at least around certain portions of the foil assembly is formed laterally on the foil assembly. Fixing by a tongue-and-groove system advantageously makes it possible, in particular, to ensure that the exhaust gas flows through the entire cross section of the conical honeycomb body and is fully passed on into a cylindrical honeycomb body disposed upstream or downstream, as appropriate.
With these solutions that are preferred according to the invention, the conical foil assembly can consequently be fixed in the conical casing tube in a simple and effective manner and can be produced at low cost, while increasing its mechanical stability in the finished state.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a conical honeycomb body and a method of producing it, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.